Ferrite cores, powdered metal cores and high energy product magnets such as samarium cobalt and neodymium-iron-boron magnets have certain advantageous magnetic and electric field properties making them ideal for use in certain types of electronic components and circuitry. These types of materials are frangible, yet the materials can be fabricated into a variety of shapes and generally exhibit good mechanical characteristics under compression loads. However, these frangible materials are generally weak in tensile strength, tending to crack or fracture when subject to relatively modest tensile loading, binding loads or impact loading. Cracks and fractures within the fabricated frangible materials can substantially decrease the beneficial magnetic and electric field properties, negatively impacting their desirable characteristics. Thus, maximum utilization of these types of frangible materials requires consideration of, and accommodation for, their limiting physical properties.
An exemplary application which can benefit from the use of a ferrite core as part of an electronic circuit is an Electronic Identification (“EID”) or Radio Frequency Identification (“RFID”) transponder circuit used in EID or RFID systems. EID and RFID systems generally include a signal emitter or “reader” which is capable of emitting a high frequency signal in the kilohertz (kHz) frequency band range or an ultra-high frequency signal in the megahertz (MHz) frequency band range. The emitted signal from the reader is received by a “transponder” which is activated in some manner upon detection or receipt of the signal from the reader. In EID and RFID systems, the transponder generates a signal or inductively couples to the reader to allow the reader to obtain identification codes or data from a memory in the transponder.
Generally, the transponder of an EID or RFID system will include signal processing circuitry which is attached to an antenna, such as a coil. For certain applications, the coil may be wrapped about a ferrite, powdered metal, or magnetic core. The signal processing circuitry can include a number of different operational components including integrated circuits, as known in the art, and many if not all of the operational components can be fabricated in a single integrated circuit which is the principle component of the signal processing circuitry of EID and RFID devices.
For example, certain types of “active” RFID transponders may include a power source such as a battery which may also be attached to the circuit board and the integrated circuit. The battery is used to power the signal processing circuit during operation of the transponder. Other types of transponders such as “Half Duplex” (“HDX”) transponders include an element for receiving energy from the reader, such as a coil, and elements for converting and storing the energy, for example a transformer/capacitor circuit. In an HDX system, the emitted signal generated by the reader is cycled on and off, inductively coupling to the coil when in the emitting cycle to charge the capacitor. When the emitted signal from the reader stops, the capacitor discharges to the circuitry of the transponder to power the transponder which then can emit or generate a signal which is received by the reader.
A “Full Duplex” (“FDX”) system, by comparison, includes a transponder which generally does not include either a battery or an element for storing energy. Instead, in an FDX transponder, the energy in the field emitted by the reader is inductively coupled into the antenna or coil of the transponder and passed through a rectifier to obtain power to drive the signal processing circuitry of the transponder and generate a response to the reader concurrently with the emission of the emitted signal from the reader.
Notably, many different circuit designs for active, HDX and FDX transponders are known in the art and have been described in a number of issued patents, and therefore they are not described in greater detail herein. Many of the types of EID and RFID transponders presently in use have particular benefits resulting from their ability to be imbedded or implanted within an object to be identified in a manner whereby they are hidden from visual inspection or detection. For such applications, the entire transponder may preferably be encased in a sealed member, for example to allow implantation into biological items to be identified, or to allow use in submerged, corrosive or abusive environments. Accordingly, various references, including U.S. Pat. Nos. 4,262,632; 5,25,550; 5,211,129; 5,223,851, 5,281,855 and 5,482,008, disclose completely encapsulating the circuitry of various transponders within a ceramic, glass or metallic container.
For an encapsulated transponder, it is generally the practice to assemble the transponder circuitry and then insert the circuitry into the glass, ceramic or metallic cylinder, one end of which is already sealed. The open end of a glass-type cylinder is generally melted closed using a flame, to create a hermetically sealed capsule. Other types of glass, ceramic or metallic containers utilize a cap to seal the open end, with the cap glued or mechanically connected to the open ended cylinder, as discussed for example in U.S. Pat. No. 5,482,008. Furthermore, as discussed in the aforementioned patent, to prevent the transponder circuitry from moving around inside of the capsule, it is also known to use an epoxy material to bond the circuitry of the transponder to the interior surface of the capsule.
As shown for example in U.S. Pat. No. 4,262,632 (hereby incorporated by reference), the potential advantages of utilizing EID and RFID devices in biological applications, such as the identification of livestock, have been under investigation for several years. As discussed in the 4,262,632 patent, studies show that an EID “bolus” transponder suitable for placement in the reticulum of a ruminant animal will remain in the reticulum for an indefinite time if the specific gravity of the bolus transponder is two or greater, and/or the total weight of the bolus transponder exceeds sixty grams. Accordingly, for such applications, the bolus transponder generally requires a weight element as the EID circuitry can generally be very small and lightweight, requiring merely the integrated circuit and antenna and few other components. It has therefore been disclosed, for example in the 4,262,632 patent to incorporate a ferrite weight element within an encapsulant which also contains an EID transponder.
The design of a bolus transponder suitable for use in a ruminant animal may be also benefit from the appropriate use of a magnet or a ferrite core to enhance the signal transmission characteristics of the transponder while also providing the necessary weight to maintain the specific gravity of the bolus transponder at two or greater, and/or to have the total weight of the bolus transponder exceed sixty grams. In order to obtain widespread acceptance and use of the EID bolus transponder devices for ruminant animals, however, the devices must also be designed and fabricated with an understanding of the physical and economic requirements of the livestock application. Thus, while ceramic encapsulated bolus transponders suited to the reticulum environment are being investigated, the cost and fragile physical characteristics of the ceramics impact their commercial acceptance. Thus, an encapsulant for fabricating the capsule or casing for EID transponders which does not have the limitations of ceramic, glass or metallic encapsulants, particularly for bolus transponders, would be highly beneficial.